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Light induced degradation of hydrogenated amorphous silicon - Germanium alloy (a-SiGe:H) thin films
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Hydrogenated amorphous silicon germanium alloy thin films prepared by Plasma Enhanced Chemical Vapor Deposition (PECVD) with varying Germanium concentrations have been investigated in both the annealed and the light soaked state. Samples were characterized using steady state photoconductivity and dual beam photoconductivity (DBP). The Staebler-Wronski effect has been investigated by monitoring the changes in the photoconductivity, σ ph, and the increase in the sub-bandgap absorption coefficient, α. The kinetics of defect creation for different germanium contents has also been compared with those for unalloyed hydrogenated amorphous silicon films. It is found that for the films with low Ge fraction, both a decrease in the photoconductivity and an increase in α (1.0eV) show similar time dependences to those observed in a-Si:H films. However, as the Ge content increases, σ ph degrades faster and the same time dependence is not seen in the increase of α(1.0eV).